1. Field of the Invention
The present invention relates to a drive-in dowel formed as a sleeve provided with a load application element formed, preferably, as an inner thread, and having a front section formed of a plurality of expansion elements separated by longitudinal slots.
2. Description of the Prior Art
The anchoring of a known drive-in dowel is based primarily on the expansion principle. The known drive-in expansion dowel is generally formed of two parts and includes a sleeve-shaped dowel body with a conical bore and an expansion member. For anchoring the dowel in a prepared bore, the expansion member is driven into the expansion region of the sleeve-shaped dowel body with hammer blows. As a result, the expansion region of the dowel body is radially expanded and force-lockingly pressed against the bore wall. Forming the dowel of several parts can result in several problems. E.g., the expansion member can be incorrectly inserted into the dowel body bore. The expansion member can fall out of the dowel body bore and become lost. In cases when the expansion member is held outside of the bore of the dowel body, if the hammer blows miss the expansion member, it can become skewed. In order to obtain a desired holding value, high expansion forces are necessary. For keeping, despite the necessary high expansion forces, the drive-in forces small, the expansion member should have an approach angle as small as possible. To this end, the expansion member should have a relatively large length. This results in the expansion member occupying almost a half of the longitudinal extent of the dowel body. Therefore, an anchor rod, which is screwed into the inner thread, can be adjusted only in a very limited range. Because of a relatively small depth the anchor rod is screwed into the inner thread of the dowel body, a large transverse load can result in breaking of the dowel body.
As it has already been mentioned above, high expansion forces are necessary for anchoring in accordance with the expansion principle. High expansion forces lead to large distances between axes and edges of formed attachment points. Because these distances cannot always be obtained, in addition to the use of dowels based on the expansion principle, systems based on a form-locking connection are also used. The systems based on the from-locking connection make use of undercuts which are usually provided in the region of the bore bottom. The anchoring is effected with expansion tabs which are provided on the dowel body and which expand radially into an undercut to form a form-locking connection.
German Publication DE-A 35 36 518 discloses a drive-in dowel to be form-lockingly anchored in a bore provided with an undercut. The drive-in dowel consists of a sleeve provided with an inner thread and supportable on the bore bottom. The sleeve has, in its front region, a plurality of expansion elements. The expansion elements are hingedly connected with the sleeve and are formed of trailing and leading expansion tabs connected by flexors, respectively. The leading tabs extend at an acute angle toward the longitudinal axis of the sleeve and are supported on their front ends. Upon the sleeve being impact-driven into a bore, the expansion elements expand at the flexors and become engaged in the undercut. Upon being expanded, the leading expansion tabs form a flat bottom. The drive-in dowel disclosed in this German publication contrary to the conventional two- or multi-part systems with an undercut, is formed as a one-piece part and consist of a sleeve having an inner thread and expandable expansion elements. However, the one-piece drive-in dowel disclosed in German Publication DE-A 35 36 518 only then can be anchored in a bore when an undercut has been formed in the bore by a separate step. The process of forming an undercut is very time-consuming and requires use of special undercut-forming tools for forming undercuts at a required depth. At that, a precise spacing of the undercut from the bore bottom must be insured because otherwise there exists a danger that the expansion tabs would not expand or would not completely expand.
Accordingly, an object of the present invention is to eliminate the drawbacks of the conventional or known drive-in dowels. Another object of the present invention is to provide a one-piece dowel which can be anchored in bore by applying only axial hammer blows. The drive-in dowel should be capable of being form-lockingly anchored, thereby providing for small distances between axes and edges of attachment points. The drive-in dowel should be capable of being form-lockingly anchored without a need in an additional operational step requiring a special undercut-forming tool for forming the undercut at an exactly predetermined distance from the bore bottom.